1. Field of the Invention
The present invention relates to a communication cable, and more particularly to a communication cable having an improved configuration capable of high-speed transmission by restraining an alien crosstalk phenomenon between cables.
2. Description of the Related Art
Generally, a so-called UTP (Unshielded Twisted Pair) cable is widely used as a communication cable. For making the UTP cable, wires composed of a conductor made of copper or the like and a coating for insulating the conductor are twisted to make a wire pair (see FIG. 1), and about four wire pairs are collected and the coated.
Such a communication cable is classified using an identifying symbol, named Category (or, Cat.) depending on its signal transmission capability. For example, Cat.3 enables 16 MHz signal transmission, Cat.4 enables 20 MHz signal transmission, and Cat.5 enables 100 MHz signal transmission. As a higher modulating frequency is used, a greater amount of information may be transmitted. However, as a higher modulating frequency is used, crosstalk in a cable and crosstalk between cables are generated, which makes it difficult to separate signals at a receiver. Due to the reason, information transmission capability of the UTP cable has been limited to the level of about 155 Mbps (Megabit per sec).
However, along with the development of transmission equipment technique, signal degradation caused by crosstalk in a cable can be compensated by means of a compensation or cancellation method using DSP (Digital Signal Processing) or the like. Thus, Cat.5e cable may allow 1000 Mbps (or, 1 Gbps) transmission, and IEEE (Institute of Electrical and Electronics Engineers) Standards Committee has formally standardized 1000 Base-T as an Ethernet standard in 1999.
Accordingly, a high frequency is much more used for increase of transmission capability. However, as a higher frequency is used, insertion loss and crosstalk between wires around a cable are much increased in proportion thereto. Furthermore, recently, there have been attempts to use a high frequency band over 400 MHz, particularly in the range of 500 to 650 MHz, so as to obtain a Shannon capacity of 20 Gbps or above in theory, and actually up to 10 Gbps. In this case, alien crosstalk between cables becomes a vital issue.
In order to overcome the difficulty on signal separation caused by the crosstalk, a compensation equipment such as DSP and a shielded cable having an improved cable structure were conventionally used. First, in case a compensation equipment such as DSP is used, crosstalk generated in a cable may be solved, but alien crosstalk is generated, so transmission signals of adjacent cables are interfered with each other due to the effect of electromagnetic wave according to high frequency transmission, thereby making signal separation impossible.
Meanwhile, the shielded cable is basically designed for usage under poor environments, namely in a place seriously influenced by electromagnetic wave. Such a shielded cable is configured in a way that a metal film having excellent electromagnetic wave shielding characteristic is inserted therein, so that a signal to be transmitted is less influenced by crosstalk caused by electromagnetic wave even in a place where signal crosstalk is serious. FTP (Foiled Twisted Pair) cable and STP (Shielded Twisted Pair) cable are used as the shielded cable. STP is configured so that pair and sheath are respectively shielded using an aluminum film, and FTP is configured so that only sheath is shielded. In case of having an electromagnetic wave shielding characteristic by means of winding of a metal film, the cable does not cause alien crosstalk by electromagnetic wave during high frequency transmission in the range of 500 to 650 MHz, so it may allow 10 Gbps transmission in a technical aspect. However, there are following problems in replacing an existing UTP cable with FTP cable or STP cable.
First, in Europe, at least 95% of subscriber networks employ UTP cable, and STP cable is used for special purpose. Since at least 95% of relevant industries and engineers possess or study UTP cable network technique, so they have no choice but to prefer UTP cable. In addition, since STP cable has low tolerance in installation, its characteristics are seriously changed depending on installation skill of engineers and the characteristics of the system itself are seriously deteriorated even by a minute carelessness, which makes STP cable not agreeable to general users.
In addition, seeing other drawbacks related to replacement difficulty, in case a metal film is used for shielding like FTP structure, there are problems of an increased density causing increase of weight, bad flexibility, easy corrosion, and difficult processing. In addition, separate processes should be inconveniently added during cable production.